Flat-round joint in a &#34;CT&#34; or &#34;Serpentine&#34; fin core

ABSTRACT

A method of securing a plurality of oblong tubes into a plurality of circular openings in a header of a CT or Serpentine style fin core exchanger. One end of each tube is shaped into a circle, inserted into a circular opening in the header and bonded into place thus forming a Flat-Round joint.

FIELD OF THE INVENTION

[0001] The present invention generally relates to heat transfer productsusing a CT or Serpentine fin style core, including but not limited to,radiators, shell and tube type heat exchangers, charge air coolers, oilcoolers, and fuel coolers. More particularly, the invention relates to aFlat-Round joint used in a CT or Serpentine fin core.

BACKGROUND OF THE INVENTION

[0002] Currently the tube-to-header assembly of CT and Serpentine styleradiators utilizing oblong tubes use a header with oblong openings thatare typically the same shape as the tube, only slightly larger. The tubeis bonded, non-mechanically, to this header using a solder dip process,a weld process, or a brazing process. Such tube ends with an oblongcross-sectional shape will have a diameter in one direction greater thanthe diameter in another (usually perpendicular) direction, which isreferred to herein as the “major diameter” and “minor diameter”,respectively.

[0003] Creation of a tube-to-header assembly or joint is accomplished byaffixing a plurality of tubes having oblong ends into a plurality ofcorresponding oblong openings of approximately equal cross section inthe header. As shown in the prior art (e.g., U.S. Pat. No. 5,150,520 toDiRisi), the tubes are inserted into corresponding openings in theheader wall whereupon the minor diameter of the tube end is reduced andthe major diameter of the tube end is increased to create a contactingfit around the circumference of the header. Each tube isnon-mechanically bonded to a corresponding collar opening in the headerwall to form a plurality of tube-to-header joints. The collar openingsare formed in the same operation when the plurality of openings arepunched into the header.

[0004] Unfortunately, these prior art bonding processes add thermalstress to the tubes at their respective bonding locations, therebyincreasing the grain size of the tube and reducing the tensile strengthof the material at this point. A reduction in such tensile strength canresult in pressure cycle fatigue and failure. This fatigue is also aresult of the stresses applied during thermal cycling. Thermal cyclingoccurs during a cyclic change in coolant temperature, when idol coolant,initially at ambient temperature, becomes significantly hotter duringuse. During the thermal cycle, deformation of the header may occur as aresult of the weight of the heat exchanger and the coolants therein,thereby weakening the core-to-header assembly, which leads to failure ofthe bond. Furthermore, the addition of the secondary filler material,used to aid in strengthening the stressed tubes, can be a source forenvironmental concerns, such as the use of leaded solder for thesecondary filler material.

SUMMARY OF THE INVENTION

[0005] In one aspect, the invention generally features a bond between atube and a header in a heat transfer device. At least one end of thetube is generally circular so as to fit into a corresponding circularopening in the header. The circular end of the tube is then insertedinto the circular opening in the header and then a bond is formedbetween the tube and the header.

[0006] Another aspect of this invention is to provide a Flat-Round jointin either a CT or Serpentine fin core by creating a bond between acoolant tube having an oblong cross-section and a header of a heatexchange device. One end of the coolant tube is shaped into a circularcross section. The circular end of the tube is inserted into a circularopening on the header and a bond is formed between the circular tube endand the header.

[0007] Yet another aspect of this invention is to provide an improvedFlat-Round joint in combination with a coolant tube having an oblongcross-section and a header in a heat transfer device having either a CTor a Serpentine fin core.

OBJECTS OF THE INVENTION

[0008] It is, therefore, one of the primary objects of the presentinvention to provide a joint in a CT or Serpentine fin core of a heatexchange device which will substantially overcome the shortcomings ofprior art tube-to-header assemblies as described above.

[0009] Another object, of the present invention, is to provide aFlat-Round joint in either a CT or Serpentine fin core which enablesforming a bond between a coolant tube having an oblong cross section anda header.

[0010] Yet another object, of the present invention, is to provide aFlat-Round joint in either a CT or Serpentine fin core that reduces therow pitch in both the staggered and parallel style arrays.

[0011] A further object, of the present invention, is to provide amechanical bond between a coolant tube having an oblong cross sectionand a header in a CT or serpentine fin core exchanger.

[0012] In addition to the above-described objects and advantages of thepresent invention, various other objects and advantages will become morereadily apparent to those persons who are skilled in the same andrelated arts from the following more detailed description on theinvention, particularly, when such description is taken in conjunctionwith the attached drawing, figures, and appended claims.

DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is a partial oblique view of the top of the header of atube-to-header assembly used in prior art.

[0014]FIG. 2 is a partial oblique view of the side of the header, tubesand fins of a tube-to-header assembly used in prior art.

[0015]FIG. 3 is a partial oblique view of the top of the header of apresently preferred embodiment of the tube-to-header assembly.

[0016]FIG. 4 is a partial oblique view of the side of the header, tubesand fins of a presently preferred embodiment of the tube-to-headerassembly.

[0017]FIG. 5 is an oblique view of an inside sizing tool and an outsidesizing tool.

[0018]FIG. 6 shows a parallel circular opening arrangement in a header.

[0019]FIG. 7 shows a staggered circular opening arrangement in a header.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Prior to proceeding to a much more detailed description of thepresent invention, it should be noted that identical components whichhave identical functions have been identified with identical referencenumerals throughout the several views illustrated in the drawing figuresfor the sake of clarity and understanding of the invention.

[0021] Turning now to the drawings, FIGS. 1 and 2 are oblique views of aprior art type of tube-to-header assembly, generally designated 10. Thetube-to-header assembly 10 includes a header 12, a plurality of corefins 14, and a plurality of oblong tubes 16 that are secured to theheader 12 by means of a non-mechanical bond 18. The tubes 16 have amajor dimension that is several times greater than the minor dimension.This non-mechanical bond 18 is accomplished through various processes,such as welding, brazing, or solder dipping of the oblong tubes 16 intocorresponding oblong openings (not shown) in header 12. The oblongopenings in the header 12, which receive the tubes 16, are formed by apunching operation. The use of a punch for forming these openings putsan upper limit of the thickness of the header 22.

[0022]FIG. 3 is an oblique view of the presently preferred embodiment ofthe present invention. Reference number 20 generally indicates thepreferred tube-to-header assembly utilizing Flat-Round joints. Thetube-to-header assembly 20 includes a header 22 having a plurality ofcircular openings 28 formed therein that are slightly larger than oneend of coolant tubes 16. The one circular end 26 of the oblong coolanttubes 16 has been shaped into a circular cross section that is bondedinto the headers circular openings 28. The process for shaping theseFlat-Round joints is described below. Additionally, it should beunderstood by those persons skilled in the art that a generally roundtube could be used in place of such oblong coolant tubes 26. Further,such tube-to-header assembly 20 can be produced by forming a bondbetween a coolant tube 16 having a generally oblong cross-section and aheader member 22 of a heat exchange device. The header 22 has apredetermined plurality of generally circular openings 28 which have apredetermined diameter. Openings 28 are formed therein in one of a CTand a serpentine fin configuration.

[0023]FIG. 4 provides another view of the tube-to-header assembly 20.When the ends of the tubes 16 are shaped into a circular cross section,the outsides of the tubes 16 are rounded as described below. Theportions 24 of the tubes 16 next to the header 22 are also rounded asshown in FIG. 4.

[0024]FIG. 5 is an oblique view of an internal sizing tool 30 and anexternal sizing tool 32. The use of these tools is described below.

[0025]FIG. 6 shows a parallel arrangement of the circular openings 28,and FIG. 7 shows a staggered arrangement of the circular openings 28. Inthe prior art of the tube-to-header assembly 10, shown in FIG. 1, themajor diameter of the oblong tubes 16 limits the row pitch of theopenings in the header 12. This minimum row pitch includes not only themajor diameter of the tubes 16, but also the width of the non-mechanicalbonds 18. In the present invention there is essentially no minimumseparation between adjacent circular openings 28, and therefore the rowpitch can be less than that for the prior art tube-to-header assembly10. As shown in FIG. 7 the circular openings 28 can be staggered as analternative to the parallel arrangement shown in FIGS. 3 and 6.

[0026] Turning now to the process for forming the Flat-Round joint ofthe present invention, one circular end 26 for each of the tubes 16 isshaped into a circular cross section by an internal sizing tool 30 shownin FIG. 5. The lip of circular end 26 of the tubes 16 is also roundedusing an external sizing tool 32.

[0027] The circular openings 28 are formed in the header 22, and thecircular ends 26 of the tubes 16 are inserted into the circular openings28 and extend slightly out the other side of the header 12. The circularopenings 28 may also be threaded to further strengthen the Flat-Roundjoint. The mechanical bond is then formed using a rolling tool (notshown) to roll the circular end 26 of the tube 16 into the circularopenings 28 in the header 22. In the rolling process the tubes circularend 26 and the pressure of the rolling tool expands the circularopenings 28. When the rolling tool is removed, the steel header 22contracts back more than the brass tubes circular end 26 and thus aidsin forming a strong Flat-Round joint. Then the circular end 26 of thetubes 16 extending above the surface of the header 22 are removed tomake them flush with the surface.

[0028] There are several advantages the Flat-Round joint of the presentinvention. While the prior art header 12 is restricted to a maximumthickness, the header 22 of the preferred embodiment is thick enough tosupport the mechanical bond between the tubes circular end 26 and theheader 22. This thicker header reduces the deformation of the headerwhen the tube-to-header assembly is in use. Moreover, the strength ofthicker header allows longer tubes than in the prior art tube-to-headerassemblies thereby increasing the heat exchange capability of, forexample, a heat exchanger.

[0029] The Flat-Round joint shown in the preferred embodiment forms astronger bond than the prior art bond, and therefore makes it lesssensitive to operational pressure cycle heat, and therefore has fewerfailures than the prior art bonds. Also, the mechanical bonding processdescribed above for the preferred embodiment may utilize an adhesive,but it does not subject the tubes to heat as in the prior art bondingprocess, and therefore does not increase the grain size of the tube orreduce the tensile strength of the material in the tubes in the headerwhen the bond is made. Finally, the mechanical bond does not raiseenvironmental concerns when the tube-to-header bond is made since asecondary filler material is not used.

[0030] While the present invention has been described by way of adetailed description of a particularly preferred embodiment, it will bereadily apparent to those of ordinary skill in the art that varioussubstitutions of equivalents may be affected without departing from thespirit or scope of the inventions set forth in the appended claims.

We claim:
 1. A method for forming a bond, in a heat transfer device,between a tube and a header having a generally circular opening having afirst predetermined diameter formed on a first side thereof forreceiving one end of said tube, said method comprising the steps of: a)providing at least one generally circular end having a secondpredetermined diameter on said tube to fit into said generally circularopening of said header; b) inserting said one end of said tube into saidfirst side of said header; and c) forming a bond between said one end ofsaid tube and said header.
 2. The method of claim 1 wherein said tube isa coolant tube having a generally oblong cross section.
 3. The method ofclaim 1 wherein said header contains a plurality of generally circularopenings.
 4. The method of claim 1 wherein said heat exchanger includesone of a CT and a Serpentine fin core.
 5. A method for forming a bondbetween a coolant tube having a generally oblong cross-section and aheader member of a heat exchange device, said header member having apredetermined plurality of generally circular openings, having a firstpredetermined diameter, formed therein in one of a CT and a serpentinefin configuration, said method comprising the steps of: a) shaping oneend of said tube to change said generally oblong cross-section of saidtube at said one end into a generally circular cross section having asecond predetermined diameter; b) inserting said one end of said tubeinto one of said predetermined plurality of generally circular openingsformed in said header member on a first side thereof; and c) forming abond between said one end of said tube and said header member.
 6. Themethod of claim 5 wherein step (c) includes forming said bondmechanically.
 7. The method of claim 6 wherein said bond is formedmechanically by rolling said tube into said generally circular openingin said header member.
 8. The method of claim 5 wherein step (b)includes inserting said one end of said tube into said one of saidpredetermined plurality of generally circular openings formed in saidheader member until it extends at least through a thickness of saidheader member.
 9. The method of claim 8 wherein said method includes theadditional step of removing any excess portion of said tube whichextends above a second side of said header member after step (c). 10.The method of claim 5 wherein step (a) includes the step of inserting aninternal sizing tool having a generally circular cross section into saidone end of said tube.
 11. The method of claim 10 wherein step (a)includes the step of shaping an outer surface of said one end of saidtube with an external sizing tool having a generally hollow circularcross section.
 12. The method of claim 5 wherein said method includesthe additional step of forming threads in a surface of each of saidpredetermined plurality of openings formed in said header member. 13.The method of claim 5 wherein said method further includes the step offorming said openings in said header member in a staggered arrangement.14. The method of claim 5 wherein said method further includes the stepof the forming said openings in said header member in substantiallyparallel rows.
 15. The method of claim 5 wherein said firstpredetermined diameter is slightly larger than said second predetermineddiameter.
 16. The method of claim 5 wherein step (a) includes using anadhesive in forming said bond.
 17. In combination with a coolant tubehaving a generally oblong cross-section and a header member in a heattransfer device having one of a CT and a serpentine fin configuration,the improvement comprising: a) one end of said coolant tube having agenerally circular cross section having a first diameter; b) a circularopening in a first side of said header having a second diameter throughwhich said generally circular end of said tube extends so as to beapproximately flush with a second side of said header opposite saidfirst side; and c) a mechanical attachment between said tube and saidheader.
 18. The combination of claim 17 wherein said opening is one of aplurality of openings arranged in substantially parallel rows.
 19. Thecombination of claim 17 wherein said opening further is one of aplurality of openings arranged in staggered rows.